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West Nile virus

West Nile virus is a disease spread by mosquitoes. The condition ranges from mild to severe.

Causes

West Nile virus was first identified in 1937 in Uganda in eastern Africa. It was first discovered in the U.S. in the summer of 1999 in New York. Since then, the virus has spread throughout the U.S.

Researchers believe West Nile virus is spread when a mosquito bites an infected bird and then bites a person.

Mosquitoes carry the highest amounts of virus in the early fall, which is why more people get the disease in late August to early September. As the weather becomes colder and mosquitoes die off, there are fewer cases of the disease.

Although many people are bitten by mosquitoes that carry West Nile virus, most do not know they have been infected.

Risk factors for developing a more severe form of West Nile virus include:

Conditions that weaken the immune system, such as HIV/AIDS, organ transplants, and recent
chemotherapy

Chemotherapy

The term chemotherapy is used to describe cancer-killing drugs. Chemotherapy may be used to:Cure the cancerShrink the cancerPrevent the cancer from ...

Stiff neck

Exams and Tests

Signs of West Nile virus infection are similar to those of other viral infections. There may be no specific findings on a physical examination. About half of people with West Nile virus infection may have a rash.

Mosquito, adult feeding on the skin - illustration

There are many different species of mosquito, which can carry some of the world's most common and significant infectious diseases, including West Nile, Malaria, yellow fever, viral encephalitis, and dengue fever. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, adult feeding on the skin

illustration

Mosquito, adult - illustration

This illustration shows an adult southern house mosquito. This mosquito feeds on blood and is the carrier of many diseases, such as encephalitis, West Nile, dengue fever, yellow fever, and others. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, adult

illustration

Mosquito, egg raft - illustration

Mosquitoes of the Culex species lay their eggs in the form of egg rafts that float in still or stagnant water. The mosquito lays the eggs one at a time sticking them together in the shape of a raft. An egg raft can contain from 100 - 400 eggs. The eggs go through larval and pupal stages and feed on micro-organisms before developing into flying mosquitoes. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, egg raft

illustration

Mosquito, pupa - illustration

These are mosquito pupa. This is another stage in the development of the mosquito. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, pupa

illustration

Meninges of the brain - illustration

The organs of the central nervous system (brain and spinal cord) are covered by connective tissue layers collectively called the meninges. Consisting of the pia mater (closest to the CNS structures), the arachnoid and the dura mater (farthest from the CNS), the meninges also support blood vessels and contain cerebrospinal fluid. These are the structures involved in meningitis, an inflammation of the meninges, which, if severe, may become encephalitis, an inflammation of the brain.

Meninges of the brain

illustration

Mosquito, adult feeding on the skin - illustration

There are many different species of mosquito, which can carry some of the world's most common and significant infectious diseases, including West Nile, Malaria, yellow fever, viral encephalitis, and dengue fever. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, adult feeding on the skin

illustration

Mosquito, adult - illustration

This illustration shows an adult southern house mosquito. This mosquito feeds on blood and is the carrier of many diseases, such as encephalitis, West Nile, dengue fever, yellow fever, and others. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, adult

illustration

Mosquito, egg raft - illustration

Mosquitoes of the Culex species lay their eggs in the form of egg rafts that float in still or stagnant water. The mosquito lays the eggs one at a time sticking them together in the shape of a raft. An egg raft can contain from 100 - 400 eggs. The eggs go through larval and pupal stages and feed on micro-organisms before developing into flying mosquitoes. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, egg raft

illustration

Mosquito, pupa - illustration

These are mosquito pupa. This is another stage in the development of the mosquito. (Image courtesy of the Centers for Disease Control and Prevention.)

Mosquito, pupa

illustration

Meninges of the brain - illustration

The organs of the central nervous system (brain and spinal cord) are covered by connective tissue layers collectively called the meninges. Consisting of the pia mater (closest to the CNS structures), the arachnoid and the dura mater (farthest from the CNS), the meninges also support blood vessels and contain cerebrospinal fluid. These are the structures involved in meningitis, an inflammation of the meninges, which, if severe, may become encephalitis, an inflammation of the brain.